Fixation or immobilization of wastes in cement-based materials, commonly called grouts is an important waste management method. Formulations prepared by mixing an aqueous hazardous waste material with a dry-solid blend consisting of cement, fly ash, clays, etc., are commonly referred to as grouts. Grout properties of importance in waste immobilization variously include the rheologic properties of freshly mixed grouts, the structural strength of cured grouts, the leach properties of cured grouts and the amount of grout phase separation exhibited at various times during curing. Phase separation, a serious problem, is defined as the formation of a liquid or aqueous phase along with the grout solid phase.
For quantification purposes, the volume of liquid phase collected on the top surface of the grout is measured following prescribed procedures. The top liquid phase is referred to as drainable water and is measured as the volume percent of the initial total volume of grout plus drainable water. It is generally recognized that the volume percent of drainable water for a particular waste grout will increase for approximately 24 hours and then decrease to some limit with further lapse of time.
Most operating criteria for grout waste immobilization processes require that the drainable water decrease to zero volume percent in 28 days or less. In most processes, it is preferred that the drainable water not exceed 5 percent after the first 24 hours. Drainable water is undesirable since it may contain radioactive and/or chemically hazardous materials from the waste which are normally required to be fixed or immobilized in the grout solid phase. At the present time, it is common practice to include a specialty geleing clay such as Attapulgite-150, a crystalline hydrated magnesium aluminum silicate, in grout mixes for purposes of decreasing the volume of drainable water. The clay is added in amounts of 8 to 20 weight percent of the dry-solids blend mixed with the waste. For some wastes, the geleing clays work well, while with others they work poorly or not at all.
The fixation of waste materials in grouts is an old process. In Oak Ridge National Laboratory Publication TM-9680/PI, Fixation of Waste Materials in Grouts. Part 1: Empirical Correlations of Formulation Data, O. K. Tallent et al., March, 1986, several compositions of grout were investigated and the properties of the grout compositions were measured and empirically analyzed. This publication discloses the use of grout compositions having a dry-solid blend which includes Portland Cement, Kingston fly ash, Attapulgite-150 clay and Indian Red pottery clay, an illitic clay which has the general formula (OH).sub.4 K.sub.x (Al.sub.4 Fe.sub.4 Mg.sub.4 Mg.sub.6)(Si.sub.8-x Al)O.sub.20. Various compositions including these four ingredients were used to immobilize certain industrial wastes containing sulfates, nitrates, hydroxides and carbonates. Various formulations of the dry-solid mix were tested to optimize the properties of the grout compositions. In addition, this publication gives a detailed account of the methods used in measuring the properties of grout compositions. It was found that the drainable water could be minimized to an extent by incorporating significant amounts of the Attapulgite-150 clay. However, in some of the formulations examined in this publication, there existed a significant amount of drainable water after 28 days of curing.